Face plates for cathode ray tubes are usually a layer of a phosphor powder in a binder settled onto a glass plate. Electrons strike the phosphor layer resulting in emission of light. A disadvantage of these powder layers is their susceptibility to damage when high energy electron beams are used to obtain high light outputs. In addition under the latter conditions the glass face plate can be damaged.
Attempts at overcoming this disadvantage include the use of a thin single crystalline film grown onto the surface of the glass. This gives increased burn resistance but produces multiple reflections within the film and hence poor performance.
Another way of employing a phosphor layer is described in G.B. Pat. No. 2,094,823 B and G.B. Pat. Application No. 2136195A. In the former a dried powder layer is fired at 1,350.degree. C. for 8 hours to give a ceramic layer. In the latter specification powdered phosphor is held under pressure, e.g. 15 hectobar, in a mould whilst heated to 1,350.degree. C. The resultant ceramic can be cut and polished and used as a cathode ray tube face plate.
Thermoluminescent plates may be used in radiology apparatus. This is described for example in G.B. Patent Application No. 83 27883, now abandoned. A plate of thermoluminescent material is exposed to an X-ray pattern in the same manner as X-ray photographic film. The plate is heated and radiates visible light corresponding to the X-ray pattern. This visible light is of low intensity and needs to be detected by a sensitive detector such as a photomultiplier. Subsequent heating clears the pattern and the plate can then be reused.
Various detector materials can be used. For example single crystal materials such as lithium tetraborate, and doped with copper or manganese, etc.; or recrystallized glass. The detector plate can be a single large plate or a mosaic of smaller plates. In all cases the cost of a detector plate is high. Also it is difficult to produce a plate sensitive enough by the above processes.
Scintillators are used in various systems to provide detection of X-rays. For example a sheet of scintillator material can be used as a backing for X-ray film to enhance the image formed on the film on exposure to an X-ray pattern.
The invention provides luminescent plates capable of production in quite large sizes e.g. up to 50.times.50 cms at relatively low cost.